Standby Generator backfeed in case of ATS failure

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FaradayFF

Senior Member
Location
California
Hi Guys,

I've got a standby generator at a maintenance facility that is used to provide backup in case utility supply fails. I'm thinking about possible backfeed in case the ATS fails. How concerned should I be about this possibility, the Automatic Transfer Switches are known to be reliable devices? Is there a way to safeguard against this unlikely event?

I think there would have to be two events happening - ATS switching mechanism fail AND simultaneously ATS issuing an erroneous start signal to the generator. The chance of both happening concurrently is extremely unlikely..I guess I answered my own question..

Thanks,
EE
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I'm thinking about possible backfeed in case the ATS fails. How concerned should I be about this possibility, the Automatic Transfer Switches are known to be reliable devices? Is there a way to safeguard against this unlikely event?
Transfer switches are designed for backfeed to be physically impossible. That's why there is a mechanical interlock in addition to the control system.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
If you have wired it properly, there is no way for one* ATS to fail in a way that would put energy from the generator to the grid or vice-versa. If the ATS fails to transfer to the Generator source, but starts the generator, the generator power just doesn't get to your loads, it doesn't go to the grid. Likewise if the generator is running and the ATS is putting power to your loads, then switches to the grid source without turning off the generator, still, the generator is isolated from everything and just wastes fuel.

*The only way for any back feed to happen is if you have multiple generators and ATS with multiple failures, as can happen with a Main-Tie-Main switchgear setup with separate generators for each source. But you would have to have two ATS failures PLUS the tie breaker closed.
Drives-Eaton-2-106-04-2015-fig1.jpg
 
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